Jason Preston's EatSleepPublish posting identifies some principles and practices designed to rein in the concerns about Associated Press and its intentions to target blogs using its content.
Preston has some fairly straightforward ideas: Make a blog with more than $250k in revenue subscribe, leave the others alone. The principle he invokes is a sound one: Don't harass the small fry but be direct with those clearly attempting to (and succeeding at) making money off your content without paying for it. In other words, separate the enthusiastic fan from the enthusiastic entrepreneur.
The only concern I'd have about such an approach is the way blogging firms could diversify their holdings to avoid a fee, much in the way they might to avoid a large tax bill. But that's for a brighter mind to figure out.